You have AC current running thru the video cable shield. The "ground" at the camera is slightly above or below the "ground" at the monitor. This can be fixed by using a video isolation transformer AKA ground loop isolation transformer.
OK, the world hansn't ended yet so I'm going to bore you with, yes, "VIDEO TRIVIA" Back in the day, before that new-fangled color TV, vertical scan rate was 60Hz. The even and odd fields of 262.5 lines each, make up the 525 lines of a 30Hz frame. This design eliminated "flicker". 60Hz X 262.5 = 15750Hz, which was the horizontal scan rate. But now, with NTSC 3.58, the horizontal scan rate is really 15,734 Hz. and the vertical scan rate is really 59.94 Hz. That creates a .06Hz beat frequency with any AC hum. I would argue that the lines are walking up your screen more than running since it might take more than 8 or 16 seconds to make a round trip.
More trivia. The color burst frequency you always hear of as being 3.58MHz, is really 3.579545MHz. More importantly, four times that is 14.31818MHz. This frequency produces 70nS read and write clocks that are used in time base correctors and frame synchronizers used in the U.S.A. and other countries using NTSC 3.58. These are used in TV studios or post-production facilities to prevent nasty horizontal or color shifts. Video is written into memory using a write clock that is phase locked to the burst of the video source. It is read from memory using a read clock phase locked to a house reference. If everything is timed in correctly, the house is said to be in SC-H (subcarrier, horizontal) phase.
WAKE UP! This is something most will never hear about. You generally think of there being 30 frames of video. But for editing purposes, there are really 15 color frames a second. The frames are referred to as "A" & "B". If you do an edit between two sources as A,B,A,B/B,A,B,A,B..., you will get a nasty shift at the edit point. That is because the burst phase is 180 degrees out.
So what do the last two paragraphs have to do with your problem? Nothing! I'm just happy the world as we know it hasn't ended. I hear Heaven might use PAL or SECAM and I couldn't find work there. I had a similar problem to yours when I installed a sat. Rx. inside our existing audio facility and had to run video and audio to our new facility router. The video hum bar was terrible until I ran it through an equalizing distribution amplifier. I didn't really need the EQ. but it used an isolated BNC connector on the input and a differential amplifier. I posted this in a couple other threads. An isolation transformer on either the video source or monitor power supply would fix it. I don't think that transformers in the video path hold your answer if you're talking composite video. Joe
Another approach is to isolate the video source that is causing the hum bars, from the local ground. THIS DOES NOT MEAN CUT OFF THE GROUND PIN! If it is a camera, mount the camera base on a piece of wood. If it is powered by a plug in power supply, check to see if there is a ground lift jumper or switch.
Verify that the earth grounds at the outlets feeding the video equipment are connected to the same grounding system and they are at the same potential to each other.